Why isn't there any transportation in Fallout 3?

Why would there be? Everything's been destroyed in the Great War. Only the Enclave have access to any kind of mechanical transportation in the game (the Vertibirds) and maybe the BoS (I have to wonder how they traveled from the West Coast).

I would think it'd be interesting to see some functioning motorcycles since there's certainly enough of them lying around to build a whole one, but this would cause about the same issues horses in Oblivion caused.